With the development of the liquid fuel engine technology, high power density is greatly needed. The higher efficiency of cylinder combustion process can enhance the engine power, wherein the most important factor is to optimize the fuel injection process.
Taking diesel engine as an example, with the enhancement of the power, the power scope becomes wider, which needs to enlarge the range of fuel injection quantity. Large fuel injection means to require large fuel injector nozzle area. Under the condition of small fuel injection quantity or idling, the large fuel injector nozzle can cause relatively large fuel injection error which may lead to speed fluctuation. However, if we accurately control the fuel injection quantity at the low speed, we will not get the maximum fuel injection. The highly-intensified diesel engine should embrace the real-time flexible adjustable characteristics at the process of high pressure injection so as to improve the dynamic characteristics of the engine. As for the mainstream oil supply system it is a challenge to accurately control the large scope of fuel injection quantity and improve the cycle responding characteristics of the fuel injection system.
The high pressure common rail fuel supply system can flexibly regulate the fuel injection. But the larger volume of the common rail cavity leads to slower cycle response speed that is unable to regulate injection starting pressure in cycles. The electronic unit pump adopts the mode of one cylinder to one pump which accumulates the high pressure only at the injection stage. It can obtain the high injection pressure and enjoy system reliability. But the disadvantages are also obvious: the injection pressure and fuel injection law can not be adjusted, the injection pressure relates with cam speed which cannot match the injection characteristic for high speed and low speed simultaneously. It can be concluded that neither high pressure common rail fuel supply system nor electronic unit pump can meet the large fuel injection scope of the highly-intensified diesel engine and high requirements for the cycle response characteristic.
Thus, we need a new type of fuel injection technology to optimize the fuel injection process to solve the above problems.